Recently, various attempts have been made to develop a new transmission system for increasing fuel efficiency. Among the attempts, a double clutch transmission (DCT) has received attention as a new transmission system. Currently, since the DCT exhibits excellent fuel efficiency and power conversion performance, the DCT is applied to various types of vehicles.
Since the DCT has a structure in which input shafts (hollow shafts) for transmitting power are placed in parallel, the transmission structure can be reduced in length. In particular, since speed change is performed through two clutches, the DCT has excellent speed change efficiency. That is, an input shaft for transmitting power of an engine is separated into two shafts, an odd gear is arranged on one shaft, and an even gear is arranged on the other shaft. Then, the two clutches are alternately operated to change speed.
As the number of speed stages increases, a transmission applied to a vehicle as well as the DCT can not only smoothly change speed, but also improve fuel efficiency. Thus, much research has been conducted to increase the number of speed stages.
In order to increase the number of speed stages, gear trains must be added for a desired speed stage. In this case, however, the whole length as well as the entire weight of the transmission is inevitably increased.
Thus, there is a demand for a transmission which is capable of increasing the number of speed stages through a simple structure without increasing the entire weight of the transmission.